This invention relates generally to audio amplifiers for electric guitars or the like and, more particularly, to a filter circuit for such an amplifier for selectively altering the amplitude and phase signals within selected, narrow frequency bands of the signal being amplified.
In conventional guitar amplifiers, the input signal from the electric pickup of the guitar is applied to a preamplifier which acts as an input buffer. Thereafter, the preamplified signal is coupled to a volume control potentiometer, and the volume controlled signal from the potentiometer is then coupled to three filters respectively responsive to bass, middle and treble, manual controls for selectively varying the frequency response of the amplifier. These controls enable the operator of the amplifier to selectively emphasize at least one of these three ranges of the frequency spectrum of the musical instrument.
However, the ear is most sensitive to audible signals having a frequency in the range from 1 kHz to 4 kHz. Sustained high energy in any wide segment of this band results in what is commonly referred to as aural fatigue. This is due to the subjective hearing experience being more responsive to changes in sound than to absolute levels. The problem of aural fatigue is not solved by the conventional bass, middle and treble frequency response controls, for each control emphasizes its associated wide band range of the frequency spectrum. There is, therefore, a need in guitar amplifiers and the like for a circuit which will eliminate or reduce this aural fatigue problem.